Engineered hardwood flooring has a relatively thin hardwood top plate (e.g. about 1/8 of an inch) glued to a top surface of a core plank. The core plank is typically about six inches wide and about seven or eight feet long. It is typically 1/4 to 1/2 inch thick, and normally made of plywood, fiberboard, particle board, lumber board, OSB. The top of the hardwood top plate is coated with a polyurethane or similar finish to protect the luster and beauty of the hardwood. The core plank has tongue and groove construction to facilitate installation. The hardwood top plate is manufactured by gluing and clamping two inch wide hardwood strips to form a planar surface. The hardwood top plate is then glued to a top surface of the core plank. A backing layer (e.g., wood fiber, hardwood, softwood, veneer, paper, etc.) is normally glued to the bottom of the core plank to balance the core and prevent warping. The backer also helps to seal the core plank from moisture, and help maintain structural integrity of the floor.
While plastic laminate floors can be convenient to install, the noise and appearance of repetitive printed wood grain images of such floors is not particularly appealing to many consumers. On the other hand, engineered hardwood flooring provides the luster and beauty of hardwood floors, yet is typically less expensive and more convenient to install than conventional hardwood floors. Engineered hardwood flooring is typically installed to float over the sub-floor, although it can also be attached to the sub-floor. In order to make engineered hardwood floors more comfortable to walk on and quieter, it is known in the art to provide a foam underlayment on the sub-floor before installing the engineered hardwood floor. It has been found that foam underlayments dampen floor vibrations, and reduce decibel level and duration of both low frequency impact noise (such as the sound of walking across the floor) and high frequency room noise. When used on a second story room, the foam underlayment also reduces sound transmission through the floor/ceiling into the room below. While foam underlayments often work well, it is not always practical to use foam underlayment when installing an engineered hardwood floor.
In many applications, it would be desirable for the engineered hardwood flooring plank to have inherent sound attenuation characteristics.